Washington, Nov 24 (IANS): After several failed attempts to negotiate the tough terrain of the Tibetan plateau, farming cold-tolerant barley helped humans adapt to year-round living at higher altitudes some 3,600 years ago, says a new research.

"Since 3,600 calendar years before the present, a novel agro-pastoral economy facilitated year-round living," the researchers noted in the study.

Barley is one of the most widely grown crops on the plateau even today.

"Over 3,600 years ago, only after frost-hardy and cold-tolerant barley and wheat - and perhaps sheep, too - arrived, could people continue to move higher," the researchers led by Fahu Chen and Guanghui Dong of the Lanzhou University in China were quoted as saying.

For the study, the researchers gathered archaeological artefacts, animal bones and the remains of plants at 53 sites in the north-eastern part of the plateau.

All of the sites contained the charred remains of cereal grains such as millet, barley and wheat, but the investigators found that the sites higher than about 2,500 metres contained primarily barley and not millet.

Barley may have arrived in the region as part of the same cultural exchange that brought wheat from the West, the study pointed out.

Millet was domesticated in China but is sensitive to frost. Barley and wheat, from the Middle East's Fertile Crescent, are hardier, Nature reported.

The study appeared in the journal Science.